1. Field of the Invention
The present invention relates generally to methods for fabricating photomasks which in turn are employed for fabricating microelectronic fabrications. More particularly, the present invention relates to methods for fabricating multiple masking layer photomasks which in turn are employed for fabricating microelectronic fabrications.
2. Description of the Related Art
Microelectronic fabrications are formed from microelectronic substrates over which are formed patterned microelectronic conductor layers which are separated by microelectronic dielectric layers. Common in the art of microelectronic fabrication for use when fabricating microelectronic fabrications is the use of photolithographic methods which in turn employ photomasks for defining dimensions of patterned photoresist layers which further in turn are employed for defining dimensions of microelectronic devices and patterned microelectronic layers within microelectronic fabrications.
As microelectronic fabrication integration levels have increased and microelectronic device and patterned microelectronic conductor layer dimensions have decreased, it has become common in the art of microelectronic fabrication when employing photolithographic methods which employ photomasks for defining dimensions of patterned photoresist layers which further in turn are employed for defining dimensions of microelectronic devices and patterned microelectronic layers within microelectronic fabrications to employ photomask constructions which provide for enhanced intensity resolution of a photoexposure radiation beam which is employed for photoexposing a blanket photoresist layer when forming a patterned photoresist layer. As is understood by a person skilled in the art, a class of photomask constructions which provides for such an enhanced intensity resolution of a photoexposure radiation beam employed for photoexposing a blanket photoresist layer when forming a patterned photoresist layer is the phase shift mask (PSM) class of photomask constructions.
While there exists within the art of microelectronic fabrication various types of phase shift mask (PSM) photomask constructions which effectively provide for enhanced intensity resolution of a photoexposure radiation beam passed through a phase shift mask (PSM) photomask construction for use when forming a patterned photoresist layer from a blanket photoresist layer, from a practical perspective of ease of fabrication, a particularly desirable phase shift mask (PSM) photomask construction is an attenuated phase shift mask (APSM) photomask construction. A schematic cross-sectional diagram of an attenuated phase shift mask (APSM) photomask construction is illustrated within the schematic cross-sectional diagram of FIG. 1.
As is illustrated within the schematic cross-sectional diagram of FIG. 1, there is shown an attenuated phase shift mask (APSM) photomask construction 14 comprising a transparent substrate 10 having formed thereupon a series of patterned semi-transparent masking layers 12a, 12b and 12c. Within the attenuated phase shift mask (APSM) photomask construction 14 whose schematic cross-sectional diagram is illustrated in FIG. 1, the series of patterned semi-transparent masking layers 12a, 12b and 12c is formed of a semi-transparent masking material, typically and preferably having a transmissivity of from about 3 to about 8 percent of an incident photoexposure radiation beam 16 incident upon the attenuated phase shift mask (APSM) photomask construction 14. As is further illustrated within the schematic cross-sectional diagram of FIG. 1, the incident photoexposure radiation beam 16 comprises: (1) a first incident photoexposure radiation beam 16a which passes through only the transparent substrate 10; and (2) a second incident photoexposure radiation beam 16b which passes through both the transparent substrate 10 and the patterned semi-transparent masking layer 12c. As is finally illustrated within the schematic cross-sectional diagram of FIG. 1, the patterned semi-transparent masking layer 12c is formed of a composition, and in particular of a thickness, such that subsequent to passing through the attenuated phase shift mask (APSM) photomask construction 14 whose schematic cross-sectional diagram is illustrated in FIG. 1 the first incident photoexposure radiation beam 16a and the second incident photoexposure radiation beam 16b are 180 degrees out of phase, which in turn provides the enhanced intensity resolution of the photoexposure radiation beam 16 once passed through the attenuated phase shift mask (APSM) photomask construction 14 whose schematic cross-sectional diagram is illustrated in FIG. 1.
While attenuated phase shift mask (APSM) photomask constructions are thus desirable within the art of microelectronic fabrication for ultimately providing within the art of microelectronic fabrication microelectronic devices and patterned microelectronic layers with enhanced resolution, phase shift mask (PSM) photomask constructions in general, and attenuated phase shift mask (APSM) photomask constructions in particular, are not entirely without problems in the art of microelectronic fabrication. In that regard and in particular with respect to attenuated phase shift mask (APSM) photomask constructions, while attenuated phase shift mask (APSM) photomask constructions do in fact provide a comparatively simple phase shift mask (PSM) photomask construction in comparison with other types of phase shift mask (PSM) photomask constructions, by the nature of their construction which includes a series of patterned semi-transparent layers, attenuated phase shift mask (APSM) photomask constructions also suffer from enhanced photoexposure radiation leakage in locations where such photoexposure radiation leakage might otherwise be undesirable.
It is thus in general towards the goal of providing, for use when fabricating microelectronic fabrications, photomask constructions, such as but not limited to attenuated phase shift mask (APSM) photomask constructions, with enhanced properties, that the present invention is directed.
Various methods for fabricating photomask constructions, and the photomask constructions resulting from the methods, have been disclosed in the art of microelectronic fabrication for providing photomask constructions with desirable properties for use to within the art of microelectronic fabrication.
For example, Garza, in U.S. Pat. No. 5,716,738, discloses an attenuated phase shift mask (APSM) photomask construction having an opaque border layer which attenuates spurious photoexposure of a photoresist layer which is photoexposed while employing the attenuated phase shift mask (APSM) photomask construction. To realize the foregoing object, the opaque border layer within the attenuated phase shift mask (APSM) photomask construction is formed employing an opaque photosensitive material, such as an opaque photosensitive polyimide material.
In addition, Tzu et al., in U.S. Pat. No. 5,783,337, discloses a method for fabricating an attenuated phase shift mask (APSM) photomask construction which similarly also employs an opaque border layer which attenuates spurious photoexposure of a photoresist layer which is photoexposed while employing the attenuated phase shift mask (APSM) photomask construction. To realize the foregoing object, the method employs when fabricating the attenuated phase shift mask (APSM) photomask construction a single blanket photoresist layer which is sequentially photoexposed twice with varying intensity of a focused electron beam radiation source such that incident to further processing of the twice photoexposed blanket photoresist layer there may be formed from a blanket chromium layer formed beneath the blanket photoresist layer a patterned chromium layer for use on the opaque border layer surrounding an active region of the attenuated phase shift mask (APSM) photomask construction.
Further, Chen, in U.S. Pat. No. 5,789,117, also discloses a method for fabricating a phase shift mask (PSM) photomask construction which similarly also employs an opaque border layer which attenuates spurious photoexposure of a photoresist layer which is photoexposed while employing the phase shift mask (PSM) photomask construction, but wherein there is employed only a single photolithographic sequence when fabricating the phase shift mask (PSM) photomask construction. To realize the foregoing object, the method employs a direct transfer of a pre-patterned photoresist layer to a singly patterned opaque chromium layer from which is formed the opaque border layer when forming the phase shift mask (PSM) photomask construction.
Finally, Rolfson, in U.S. Pat. No. 5,804,336, similarly also discloses a method for forming, with enhanced process efficiency, a photomask construction, such as an attenuated phase shift mask (APSM) photomask construction, with an opaque border layer which attenuates spurious photoexposure of a photoresist layer which is photoexposed while employing the photomask construction. To realize the foregoing object, the method employs an electrochemical plating of at least one of: (1) a first metal layer which forms the opaque border layer within the photomask construction; and (2) a patterned second metal layer which forms an active region of the photomask construction.
The teachings or each of the foregoing related art references is incorporated herein fully by reference.
Desirable in the art of microelectronic fabrication are additional methods and materials which may be employed for forming for use when fabricating microelectronic fabrications photomask constructions, such as but not limited to phase shift mask (PSM) photomask constructions, further such as but not limited to attenuated phase shift mask (APSM) photomask constructions, with enhanced properties.
It is towards the foregoing object that the present invention is directed.
A first object of the present invention is to provide a method for forming, for use when fabricating a microelectronic fabrication, a photomask construction, such as a phase shift mask (PSM) photomask construction, further such as an attenuated phase shift mask (APSM) photomask construction.
A second object of the present invention is to provide a method in accord with the first object of the present invention, wherein the photomask construction is fabricated with enhanced properties.
A third object of the present invention is to provide a method in accord with the first object of the invention and the second object of the invention, which method is readily commercially implemented.
In accord with the objects of the present invention, there is provided by the present invention a method for fabricating a photomask construction. To practice the method of the present invention, there is first provided a transparent substrate. There is then formed over the transparent substrate a blanket first masking layer. There is then formed over the blanket first masking layer a blanket second masking layer. There is then formed over the blanket second masking layer a patterned photoresist layer having an active patterned region and a border region adjoining the active patterned region. There is then etched, while employing a first etch method and while employing the patterned photoresist layer as a first etch mask layer, the blanket second masking layer and the blanket first masking layer to form a patterned second masking layer and a patterned first masking layer. There is then irradiated, while employing a cutout mask, at least a portion of the active patterned region of the patterned photoresist layer such that at least the portion of the active patterned region of the patterned photoresist layer is removed from over the transparent substrate while at least a portion of the border region of the patterned photoresist layer is not removed from over the substrate to thus form from the patterned photoresist layer a further patterned photoresist layer which leaves exposed a portion of the patterned second masking layer. There is then etched, while employing a second etch method, the portion of the patterned second masking layer exposed beneath the further patterned photoresist layer to form a further patterned second masking layer. Finally, there is then stripped from over the transparent substrate the further patterned photoresist layer.
There is provided by the present invention a method for forming, for use when fabricating a microelectronic fabrication, a photomask construction, such as a phase shift mask (PSM) photomask construction, further such as an attenuated phase shift mask (APSM) photomask construction, wherein the photomask construction is provided with enhanced properties. The present invention realizes the foregoing object by employing when fabricating the photomask construction a cutout mask for selectively further irradiating a portion of a patterned photoresist layer in turn formed over a patterned second masking layer in turn formed over a patterned first masking layer such that there may be formed from the patterned photoresist layer a further patterned photoresist layer which serves as an etch mask for forming from the patterned second masking layer a further patterned second masking layer which within the context of the preferred embodiment of the present invention provides an opaque border layer within an attenuated phase shift mask (APSM) photomask construction.
The method of the present invention is readily commercially implemented. As will be illustrated within the context of the Description of the Preferred Embodiment which follows, the present invention employs methods and materials as are generally known in the art of microelectronic fabrication. Since it is a specific ordering of methods and materials which provides at least in part the present invention, rather than the existence of specific methods and materials which provides the present invention, the method of the present invention is readily commercially implemented.